It is well known to employ static discharge elements in connection with aircraft structures so as to provide for the elimination of static electrical charges accumulated thereon. Such accumulation or build up of electric charges may prove hazardous, e.g., as in the case of the build-up of the static charges in the vicinity of the fuel tanks of the aircraft. In addition, static charge accumulation can also interfere with the radio communication operations or other amplitude modulated equipment. Such communication interference creates a particularly hazardous situation during flight operations which include take-off and landing of the aircraft since it is necessary that the aircraft be in constant communication with ground control and/or other aircraft during flight operations.
Typically, known static discharge elements are constructed of rod-like configurations which extend from a surface portion of an airplane. However, such protrusions increase drag and furthermore are subject to breakage not only as a result of the additional stress to which they are subjected during flight but also by the inadvertent mishandling of the ground personnel during a routine maintenance operation. One such typical static discharge element is shown in U.S. Pat. No. 2,466,311 which describes a static discharger attached to the trailing edge of a wing as shown in FIG. 4 therein. In particular, the '311 patent describes the use of a fibrous surface of a semi-conducting material at static discharge locations on an aircraft. FIGS. 3 and 4 of the '311 patent illustrate a layer of cloth or other fibrous material having separate free fibers cemented about a curved wing edge. The cloth is impregnated with microscopic metallic particles so that the cloth becomes semi-conductive.
U.S. Pat. No. 2,536,818 describes a discharging element wherein the discharging tip consists of a bundle of glass fibers or threads made electrically conductive. U.S. Pat. No. 2,933,732 provides a device such that the discharge allegedly occurs at a null point of the radio field and thus does not appreciably couple to the receiver antenna. In U.S. Pat. No. 3,106,663, the current density field is made perpendicular to the electric field so as to minimize the noise current in an antenna. In both the '732 and the '663 patents, however, the final discharge points are metallic pins or rods. In particular, the '732 patent describes a metal overlay attached to a wing tip or edge but which has a trailing edge of a sufficiently large radius to insure no discharge therefrom except at metal points. In U.S. Pat. No. 3,034,020, the discharger includes a group of fine wires.
U.S. Pat. Nos. 3,480,231; 3,482,802 and 3,498,572 are directed to a combination of an insulating material and conductive coating to provide protection for aircraft and associated components against lightning strikes. The conductive coating is bonded to the skin of the craft and covers the insulating material to permit any charge buildup to run off into a dispersal or charge dissipating area. The insulating material can be either a ceramic or a plastic.
U.S. Pat. No. 3,755,713 describes a typically nonconductive aircraft panel to which a wire mesh material is applied. The wire mesh is electrically connected to the metallic structure of the craft. When struck by lightning the wire mesh fuses and dissipates the energy without damage to the panel.
U.S. Pat. Nos. 3,906,308 and 3,989,984 provide lightning protection by use of dielectric materials in the form of coatings or layers placed over an aircraft surface. However in the '984 patent, the layers of dielectric material are coated by a metallic material which is provided to receive the lightning strike. In the '308 patent the dielectric material is applied to the composite panels or structure of the aircraft and is provided with metal bars or ribs as illustrated in FIGS. 9 and 10 therein for the purpose of attracting the swept-stroke and restrike lightning current.
However, notwithstanding the improvements which the above-identified patents offer, the devices disclosed therein are still subject to the aforementioned limitations of the prior art. In particular none of the above-mentioned patents disclose the use of a static discharge material, constructed preferably in the form of a flat platen, which is electrically insulated from the skin of the aircraft but for a conductive coating or but for a portion thereof contacting the conductive surface of the aircraft which permits charges to flow onto the discharging material to be discharged therefrom. Rather, the '311 patent, for example, describes a layer of cloth which is directly secured to the trailing edge of a wing. Of the next four patents noted above, these relate to conventional static dischargers which employ metallic pins or rods to discharge any static accumulations. Finally, with respect to the remaining six patents described above, the dielectric or insulating material provided is not used for dissipating static charges. Furthermore, in most of these latter six patents, the metallic coatings would prohibit such a direct discharge.
The subject application discloses an inventive static discharger which overcomes the above-noted limitations of the prior art and provides a performance not previously attainable by these known devices.